The ever progressing LSI technology has allowed higher information processing speed and larger integration scale. As a result, microprocessors are showing higher performance and memory chips are having larger capacities at rapid paces. Further, the high functions of these LSIs are already used in presently commercially available diverse electronic equipments such as digital home electronics for mainly presenting image information. Those electric equipments are personal computers, hard disc recorders, DVD recorders, etc.
In the conventional signal transmission over relative short distances, for example, between boards in each equipment or between chips on each board, electric signals are used, but further speedup and further densification are already difficult. For (1) further speedup, the signal delay due to the CR (C=electrostatic capacity of wiring, R=resistance of wiring) time constant of wiring is a problem, and for (2) further densification of electric wiring, EMI (Electromagnetic Interference) noise and inter-channel crosstalk are problems.
One of the technologies for solving these problems is optical wiring (optical interconnection) technology. Optical wiring can be applied to various places such as between equipments, between boards in an equipment, or between chips in a board. Above all, for signal transmission over short distances such as between chips, it is favorable to use an optical signal transmission system in which an optical wiring layer for waveguiding optical signals is formed on the surface of a substrate mounted with chips or as an inner layer.
Such an optical signal transmission system needs a light emitting device for converting electric signals into optical signals, a light sensing device for converting optical signals into electric signals, ICs for giving and receiving the electric signals used for controlling the light emitting device and the light sensing device, etc. and also the power supply to these devices. On the other hand, for the signal transmission that can be performed at a relatively low speed using low density wiring, the use of electric signals is mostly more advantageous. Therefore, in the wiring substrate, it is also necessary to form electric wiring on the surface of the substrate or as an inner layer. That is, an optoelectronic circuit board in which both optical wiring and electric wiring exist together is necessary.
The resin compositions used for optical wiring include polysilanes (see Patent Document 1), polysiloxanes (see Patent Document 2), fluorinated polyimides (see Patent Document 3), silica gel-polystyrene composite materials (see Patent Document 4), fluorinated acrylic polymers (see Patent Document 5), etc. None of the materials is adequate for integration with an electric wiring board for any of such reasons that the heat treatment temperature for solidification is too high, that heat resistance is insufficient, and that the thermal expansion coefficient is too large.
Optical wiring materials (optical waveguide materials) consisting of an inorganic filler and a resin include those containing titanium oxide, aluminum oxide or silica, etc. as the inorganic filler (see Patent Documents 6 and 7). However, they have such problems that the size of the particles used is large, and/or that since the refractive index of titanium oxide or aluminum oxide is larger than that of the resin, the Rayleigh scattering owing to the particles is large, hence as a result, the optical propagation loss is likely to be large.
As a hybrid optical wiring substrate having electric wiring and optical wiring, a mode in which an optical wiring layer is laid in an insulation layer (see Patent Document 8) or the like is proposed.    Patent Document 1: JP2004-12635A (claims)    Patent Document 2: JP2004-102247A (claims)    Patent Document 3: JP4-328504A (claims)    Patent Document 4: JP11-109154A (claims)    Patent Document 5: JP10-333105A (claims)    Patent Document 6: JP2000-44811A (claims)    Patent Document 7: JP2002-277664 (claims)    Patent Document 8: JP2002-6161A (claims)